The present invention concerns a unique system for separating a dispersed liquid of lower specific gravity, such as oil, from a carrier liquid having a higher specific gravity, such as water, in which it is entrained, while simultaneously separating from the carrier liquid coarse to fine solids dispersed throughout the liquid. The system of the present invention was devised to solve longstanding water pollution problems caused by discharging into harbors or upon the high seas, contaminated water used to flush ships' bilges, bunker fuel tanks and oil cargo tanks. International regulations in effect prohibit the discharge of such waste water containing more than 100 parts per million of oil contaminant. The present invention has been successfully and continuously demonstrated with discharge levels of contaminant no greater than 10 parts per million.
The system of the invention has been designed to provide the following advantages:
A. Minimum system size; PA1 B. The ability to overcome with high-g and shear forces, the surface and ionic forces in oil-surfactant mixtures, leading to improved separation efficiency; PA1 C. Insensitivity of the final separation to ship motion, because of the high-g separation forces used; PA1 D. Insensitivity to large fluctuations in effluent quality; PA1 E. No requirement for replaceable or regenerable media or items; PA1 F. Insensitivity to air entrainment in the final separation; PA1 G. Opportunity for automatic system backflushing without skilled operators and without the danger of system damage.
Accordingly, the inventive system not only solves quite uniquely the problem of reducing contamination in discharge flow to the aforementioned level but uniquely provides a system design which is most compact in size and which uniquely integrates the functions of related portions of the system. The overall system consists of three basic levels of separation. The first or primary separator is designed to maintain an oil/water interface and to reduce any high free oil loading in the effluent to a dispersed lower concentration prior to its entry into subsequent levels of separation. The second separation unit continuously removes solids that would otherwise hinder the collection of fine oil particles by causing premature clogging of the final separator. The centrifugal separator first separates find solids and larger oil particles and then coalesces and separates the remaining oil to further reduce the oil concentration in the effluent to below the specified 10ppm.